Parathyroid hormone-related peptide (PTHrP) is a recently discovered hormone with 3 predicted isoforms containing 139-173 amino acids. It is secreted by many tumors, and interacts with specific PTH receptors. PTHrP production in the cancer patient causes hypercalcemia of malignancy, which results to complications in the response to various therapeutic strategies and leads to excess morbidity in patient population. Antibodies capable of distinguishing among various isoforms of PTHrP would be a valuable tool for probing the biology of this hormone but are also unavailable. We propose to develop a panel of antibodies with specificity for several epitopes spread over the molecule. These antibodies will then be used to develop specific immunoassays for measuring the different PTHrP isoforms. This effort should result in the development of research tools with important diagnostic and therapeutic applications.